major occurrence in the study area, such as montmorillonite and 
kaolinite. Both methods showed an east-west zonation in the 
alteration at Paramount and also some zoning at Bodie. The 
zonation at Paramount is more clear and, as shown by 
Tricorder, has predominantly kaolinite (both types) and 
halloysite in the western and southwestern portions and 
predominantly Na-montmorillonite in the eastern portion, with 
a dividing line coinciding with Atastra Creek. SAM also 
showed the same zonation but mapped predominantly 
kaolinite/smectite in the western and southwestern portions and 
Na- and Ca-montmorillonite in the eastern portion. In addition, 
Tricorder was able to map two types of kaolinite, plus 
halloysite, muscovite and illite. 
In the VNIR however, results from both methods were quite 
different. Pixels mapped by SAM as goethite were assigned by 
Tricorder to hematite, whereas others mapped as jarosite by 
SAM were assigned to goethite by Tricorder. Tricorder 
managed to map more pixels as minerals with diagnostic 
spectral features in the VNIR than SAM, including hematite, 
goethite, K-jarosite and cummingtonite. 
Spectral analysis of samples from selected sites confirmed the 
Tricorder results in the SWIR region. There was a good 
coincidence of position and shape of the most important 
diagnostic features for Na- and Ca-montmorillonite, kaolinite 
(with different crystallinity), halloysite, kaolinite+smectite, 
muscovite and illite between spectral curves from ground 
samples, AVIRIS pixels assigned by Tricorder to these minerals 
and reference spectra from the USGS Spectral Library. 
Some of the characteristics of SAM, such as its availability in 
commercial image processing packages, ease of use and speed 
make it a feasible operational option for mineral mapping in 
exploration activities. Tricorder on the other hand produced 
more detailed results than SAM, and will be available for 
general use in the near future, but its complexity will demand 
some training, basic knowledge of spectroscopy and 
considerably more computing time than SAM. 
10. ACKNOWLEDGMENTS 
The authors would like to thank Robert O. Green and his 
collaborators from the AVIRIS project at NASA's Jet 
Propulsion Laboratory for the support with atmospheric 
calibration of the data and Dr. Roger N. Clark, at USGS's 
Spectroscopy Laboratory, for the use of Tricorder and fruitful 
discussions on mineral spectroscopy. A.P. Crósta acknowledges 
the support of the Desert Research Institute (DRI), University 
and Community College System of Nevada, during a sabbatical 
year as a visiting scientist, as well as the State University of 
Campinas, Brazil. This work was funded in part by Fundacäo 
de Amparo à Pesquisa no Estado de Sáo Paulo (FAPESP, 
Brazil) through Grant # 94/3474-0. 
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